The present invention relates to semiconductor processing techniques, and more particularly to a semiconductor device including a photoresist layer having improved adhesion qualities and a method for fabricating the device including the enhancement of photoresist adhesion on a substrate material.
Photoresist adhesion to substrates, in particular InGaAs and InAlAs substrates, is very poor using current methodology. The result is a reduction in the quality of photolithography processing. There have been several attempts to improve the adhesion of photoresist materials to the surface of various substrate materials, such as InGaAs and InAlAs. While many surface pretreatment options have been utilized, these conventional procedures have failed to have the adhesive durability required to complete all necessary processing steps. In particular, photoresist layers have been observed to peel away from wafer surfaces during development steps or during immersion in cleaning solutions such as an ammonium hydroxide (NH4OH) solution (10% in water). This NH4OH solution is commonly used to clean the wafer surfaces prior to subsequent processing steps such as depositions and metallization.
Several attempts have been made recently with respect to surface pretreatment options to modify the wafer surfaces in an effort to promote resist adhesion. These options have included, dehydration bakes, application of both i-line and DUV anti-reflective coatings used as thin film interlayers, standard HMDS vapor priming, and the application of several silane based organic coupling agents. However, none of these processes has improved adhesion adequately.
The current industry standard is to vapor prime wafer surfaces with hexamethyldisilizane (HMDS). HMDS is used as a means of preparing silicon wafers for the resist coating. However, HMDS is only chemically compatible with silicon and does not react in the same manner with other materials. On a silicon surface, HMDS applies, from the vapor phase, an organic monolayer which is repellant to water or other aqueous solutions such as developers or NH4OH. The water repellant nature of the film at the substrate/resist interface prevents the lifting of resist films during subsequent aqueous processing such as developing or cleaning. It is known that the contact angle of water on a surface is a good measure of water repellency of that surface. The contact angle of a water droplet on a properly HMDS primed silicon surface typically measures between 65-72xc2x0. It has additionally been found that traditional vapor priming lasts only three days until the wafers must be primed again. In addition, during the vapor priming process, wafers are typically brought to a temperature of 150xc2x0 C. for a period exceeding 30 minutes. This is objectionable for certain temperature sensitive applications.
As previously stated, other methods exist to promote adhesion of photoresist to wafers. One such method, often used to modify surfaces which are inert to vapor priming, is to use a chemical vapor deposition (CVD) process to apply a thin ( less than 500A) layer of a second material such as silicon nitride (SiN) or silicon oxide (SiO) to the surface. The deposition of this material when coupled with traditional HMDS vapor priming, provides for excellent adhesion of the resist layer to the wafer surface. However, such coatings must be later removed which can present additional problems. For example, it has been found that removal of the SiN material, generally through dry etching techniques, is very aggressive and can lead to damage of the fragile wafer epi layer.
Accordingly, it is an object of the present invention to provide for a semiconductor device that includes a surface pretreatment that promotes enhanced adhesion of a photoresist to a wafer surface.
It is another object of the present invention to provide for a semiconductor device that includes an interfacial material that promotes adhesion of a photoresist to a wafer surface.
It is still a further object of the present invention to provide for a semiconductor device that includes an enhanced photoresist adhesion in which subsequent removal of the resist and interfacial layer does not damage the underlying material surface.
It is yet another object of the present invention to provide for a method of fabricating a semiconductor device including the steps of providing for a surface pretreatment that promotes enhanced adhesion of a photoresist to a wafer surface.
It is still yet another object of the present invention to provide for a method of fabricating a semiconductor device including the steps of providing for an interfacial material that promotes enhanced adhesion of a photoresist material to a wafer surface.
These needs and others are substantially met through provision of a semiconductor device and a method of fabricating the semiconductor device including a substrate, a photoresist stack, and a carbon layer disposed between the substrate and the photoresist stack. The method of fabricating the semiconductor device includes the steps of providing a substrate having a surface, depositing a carbon layer on the surface of the substrate, and forming a resist stack on a surface of the carbon layer. The carbon layer is formed utilizing standard plasma enhanced chemical vapor deposition techniques (PECVD) or sputtering.